Calcium Imaging of Retinal Ganglion Cell Dendritic Responses to Extracellular Microelectrode Stimulation

In order to improve upon existing stimulation strategies for prosthetic vision, it is essential to assess stimulation effectiveness by measuring the responses of stimulated cells in retinal tissue. Calcium imaging has slower dynamics and lower signal-to-noise ratio than electrophysiological techniques. However, it has the ability to record responses from a large number of neurons, and is able to monitor responses from neurites too small for patch electrodes. We extended previous techniques of bulk loading RGC somata with organic calcium indicator to achieve staining of RGC dendritic processes and imaged calcium signals in retinal ganglion cell somata and dendrites simultaneously. The higher signal-to-noise ratio dendritic calcium signals make dendrites more suitable imaging regions for recording retinal ganglion cell responses to electrical stimulation protocols that are relevant to driving visual prosthetic stimulation.